Muscular strength is most rapidly developed by using various types of devices and machines which provide forces to resist movement by the user. In order to attain a rate of increase of strength and a level of strength greater than those attainable through participation in most sports and other athletic activities, relatively high resisting forces must be used. The most common presently available means for obtaining high-resistance exercise are the pulley-weight machine, the barbell, spring-action devices, and frictional devices, of both mechanical and fluid type.
The highest levels of muscular size and strength are attained through high-resistance exercise of short duration, involving only a few muscle groups at any one time. Complete isolation of individual muscles or muscle groups during exercise tends to produce the highest rate of increase in muscular strength. Exercise in which the user-exerted force is in a direction opposite to the direction of movement, called "negative exercise", is especially effective in development of strength. It is most effective when used in combination with "positive exercise", in which the user-exerted force and the movement are in the same direction.
The primary biological mechanism by which muscle fibers are induced to grow involves the accumulation of certain chemical by-products produced during intense muscular contraction. These chemicals act as a signal to the cells of the muscle fibers, and result in increases in the quantity of the protein-based muscle tissue. Exercise against light resistance has relatively little effect on muscular strength, but, if sustained for sufficiently long periods of time, it is most effective in increasing muscular endurance.
The amount of force that can be exerted by the arms or legs is highly dependent on their position and angular orientation. It depends both on the direction in which force is being exerted and on the angles of the joints. In order to obtain maximum muscular strength throughout the full range of movement, the resisting forces of an exercise must vary according to the individual's strength potential at any given position along the path of motion. Only a few very expensive machines provide for this kind of variable resistance, and these machines do not provide for variation of the functional relationship between resistance and position. Thus, they do not conform to the individual user's strength-potential curve but only to that of some "average" user. Exercise in which the resisting force does not conform to the user's particular strength-potential curve results in lower development of strength over certain segments of a path of motion as compared to that over other segments. Exercising a muscle in one position only is not effective in increasing strength at other positions.
The starting and finishing positions of an exercise motion are important. A fully extended starting position is necessary to obtain maximum intensity of muscular contraction during the exercise motion. The longest possible path of motion also allows for increases in flexibility. Due to the large variations in physical dimensions among the users, all presently available exercise machines have serious limitations in this respect.
The speed at which an exercise is performed is very important. This is because there are two distinct types of muscle fibers which comprise every skeletal muscle. The red, or slow-twitch, fibers provide forces primarily during slow movements. The white, or fast-twitch, fibers can contract only during relatively fast movements, and are used primarily in high-speed activities such as sprinting or swimming. Muscle performance at high speed cannot be improved by low-speed exercise. Nor can low-speed muscle strength be improved significantly by high-speed exercise. For these reasons, an athlete must train selectively for the particular event or activity in which he specializes.
Exercise done at relatively high speed using relatively high resistance and involving only a few muscles at one time is called isokinetics. Conventional exercise machines which use weights to provide the resisting force are not very well suited for isokinetics. Because weights have inertia, the speed of the exercise will vary greatly throughout the motion, allowing for optimum speeds and resistances only over a short segment of the full range of motion. There are some machines presently available which are primarily intended for isokinetic exercise. Most of them make use of fluid flow through an orifice, sometimes adjustable, to provide exercise in which resisting force is dependent only on speed.
In order to achieve maximum rates of strength increase, muscles must be exercised independently, and with high intensity. In order to maximize strength increases throughout a movement required in some athletic event, or, to be more specific, to maximize the integral of strength with respect to displacement along this path of motion, a high-resistance exercise must be used, and the path of motion must be very similar to that of the movement required in the event. The above facts suggest that there is a need for a machine which provides for variation of paths of exercise motion as well as resisting force. This unique capability is among the most important objectives of the invention.
Most presently available exercise machines do not even come close to providing for maximum rates of strength increase, maximum levels of strength, or optimal degrees of development of the various muscle groups, individual muscles, and parts of individual muscles. No known presently available exercise machine is suited for use by a wide range of individuals, for a wide variety of motions, and for a wide variety of exercise needs.
There is a definite need for greatly improved exercise machines in the medical field of physical rehabilitation. The same principles of muscular strength development apply to victims of accident or disease as to athletes. But rehabilitation patients are in even greater need for highly individualized and carefully regulated exercise. In rehabilitation the objectives are to achieve the greatest possible increases in muscular strength, in specific muscles and movements, in the shortest possible time. In cases involving nerve damage or paralysis a further objective of exercise therapy is the development of nerve pathways to the affected muscles. Recent studies have shown that exercise machines which are capable of actively moving a paralysis patient's arms or legs in a cyclic motion can be of great benefit in partially restoring nerve function.
Exercise equipment for rehabilitation is at about the same state of advancement as athletic equipment. In fact, standard athletics-oriented machines are often used in rehabilitation clinics. In the cases where specialized machines have been built, their effectiveness is highly limited, largely due to the fact that they are suitable for only one very specific exercise.
The complaints about present exercise machines from hospitals and clinics with rehabilitation facilities and from doctors who specialize in this field are numerous and significant. One common problem is that most machines use weights to provide the resisting force. The inertia of the weights allows the patient to throw or jerk the device in order to avoid exercising through regions of extreme weakness, precisely the regions where exercise is most needed. Other problems mentioned are lack of fine enough variation of resisting force, lack of adaptation to the patient's size, no allowance for the adjustment of the variation of resisting force with position, and general lack of adaptability to the individual patient's specific needs.